Point-Of-Use Water Heater: When It Makes Sense

A point-of-use water heater heats water right where it is used, instead of at a central heater. ENERGY STAR describes it exactly that way: water is heated very near the sink, shower or bath, and such units are often used to boost the temperature of water at a fixture that is a long way from the central water heater. It lists the situations where one is worth considering and, in the same breath, says costs and benefits should be carefully assessed first. This page sets out what ENERGY STAR, archived Department of Energy guidance and one manufacturer’s product page say, and where they stop.

What ENERGY STAR Says About When To Consider One

ENERGY STAR names three situations: new construction, additions and hot tubs. For new construction, it says to consider a point-of-use heater if the home cannot be designed to minimize losses using a more efficient central heater, such as a heat pump. For additions, when additional water load will be needed, it suggests considering one and running only cold water plumbing to the addition. For hot tubs, it says to consider one if electricity is being used for the hot water.

It also describes the qualities that make a decentralized approach more likely to save energy and money: some fixtures distant from other fixtures, low daily hot water use (its example is less than 20 gallons per day), and remote bathrooms or hot tubs. Archived DOE guidance on tankless units lists similar uses: remote bathrooms or hot tubs, and a booster for appliances such as dishwashers or clothes washers. In every case ENERGY STAR’s own caution applies: costs and benefits should be carefully assessed.

When ENERGY STAR Says It Is Not The Answer

ENERGY STAR says point-of-use units are not suitable back-ups for solar water heaters or geothermal heat pumps. Its reason is that they cannot support the full hot water demand of a household when the solar or geothermal units are not operating. That is a statement about using one as a whole-house back-up, not about using one at a single faraway fixture.

What One Maker’s Line Publishes

Rheem’s Performance Series MiniTank page shows what a compact electric unit looks like on paper. Rheem describes the units as installed at the point of use, available in 1.5, 2.5, 4.0 and 6.0 gallons, and able to deliver up to 6 gallons of hot water. Its power cord connects to a grounded 120-volt shared outlet, and Rheem states that no electrical work is required. The listed applications include a faucet or sink, boosting hot water supply, a handwashing station, an RV, a food truck, a boat, a pool house and a garage. Features listed include an adjustable temperature control from 50 to 140 degrees Fahrenheit and a temperature and pressure relief valve.

Two cautions on that page. The capacity selector on the same page lists 2, 3, 4 and 6 gallons, which does not match the 1.5, 2.5, 4.0 and 6.0 in the description, so check the specification sheet for the exact model rather than relying on either. And Rheem lists larger point-of-use electric tanks as a separate line, in 2.5, 6, 10, 20 and 30 gallon capacities. Those are one maker’s figures for those products, not a guide to what any fixture needs.

Plumbing Questions That Still Apply

A small tank is still a tank under pressure. The MiniTank includes a temperature and pressure relief valve, which is the same device our T&P relief valve guide covers, and a unit on a closed supply raises the thermal expansion question our expansion tank guide explains. A point-of-use heater does not remove either. Rheem’s adjustable control runs up to 140 degrees Fahrenheit, and State Water Heaters’ manual for its electric heaters warns that water heated to a temperature that satisfies washing and sanitizing needs can scald and permanently injure, with the elderly, children and the infirm more at risk.

What To Settle Before Buying

• Distance and use: how far the fixture is from the central heater, and how much hot water it actually uses.
• The unit’s own specification sheet: capacity, power and plumbing connections for the exact model.
• Whether a heat pump or a better-routed supply line would solve the same problem: ENERGY STAR raises this for new construction.
• The cost and benefit, assessed before purchase, as ENERGY STAR advises.

For the bigger choices, see water heater installation in Lancaster, PA and electric water heater installation.

What This Page Will Not Tell You

It will not put a dollar figure on a point-of-use unit's effect on your bills, say what size a given sink needs, or say what installing one costs. ENERGY STAR gives qualities that make a benefit more likely, not a figure, and we found no authoritative sizing rule for a fixture. We state no payback, because that needs your usage and your electric rate, and we make no claim about permit or electrical requirements for a second heater at any address.

Point-Of-Use Water Heater FAQ